Mathematical models are being developed to describe passive membrane transport through pores or intercellular spaces junctions. The Taylor-Aris dispersion analysis is extended to treat combined Brownian motion and convection in a single pore. The solute particle dimension is assumed to be large compared to that of the solvent molecules and also appreciable in size compared to the lateral pore dimension. The latter condition implies strong hindered diffusion and related solute-membrane interaction effects. A key aspect of the analysis is a generalized Einstein relation for predicting axial and radial components of the diffusivity tensor from hydrodynamics solutions for resistance coefficients. Perturbation techniques are used to obtain asymptotic solutions to the hydrodynamic equations, and the method of moments is employed to analyze the solute continuity equation. Related hydrodynamic problems are also being considered, such as flow through constricted vessels. The hydrodynamic results in combination with an analysis derived from irreversible thermodynamics, provide a predictive theory for simultaneous coupled convective and diffusive transport across porous membranes-either biological or synthetic. A review of the theoretical approaches to transport in porous membranes is included in the curriculum for the North Atlantic Treaty Organization Advanced Study Institute or Synthetic Membranes; June 26-July 8, 1983, directed by the principal investigator.